This invention relates to an internal combustion engine of either a gasoline, gas or diesel engine in the form of a four-cycle or two-cycle type which may include a mechanically-driven supercharger or a turbocharger to provide an initial compression of gases but essentially including apparatus to vary the internal compression of gases within each combustion chamber of the engine; and more particularly, the present invention relates to such an apparatus to provide a variable compression ratio in a common combustion cylinder by providing at least two pistons with separate crankshafts and means interconnecting the crankshafts to change the rotational phase relation therebetween and thereby the extent to which the gases are compressed into the combustion chamber.
As is known in the art, gasoline, gas or diesel engines designed for a two-cycle or four-cycle operation usually have a fixed compression ratio based on the displacement of gases by the movement of a piston within a cylinder closed at one end where a combustion chamber is usually formed. The fixed compression ratio is a design compromise to provide, on one hand, a sufficiently high compression ratio for a usable output from the engine; while on the other hand, avoiding excessive forces on the parts including excessive demands for bearings, rings, etc. Frequently, supercharging of gases into the cylinders, particularly in regard to diesel engines, produces a compression ratio which is too high, thereby developing excessive mechanical forces on the parts as well as an unacceptable NO.sub.x content in the combustion gases. Some prior known measures have been suggested to vary the compression ratio by using valves for the addition of gases into the combustion chamber but severe problems develop in regard to the operation of these valves. Pistons have been made extendible by a threaded connection with a connecting rod. Pistons, after resting in one position during operation for a period of time, have a tendency to freeze in that position. Another attempt to change the compression ratio is directed to changing the combustion chamber volume by moving the cylinder head and/or movably lowering of the crankshaft but excessively high forces are encountered when undertaking the design of suitable apparatus to provide movement of such parts.
The desirability for varying the compression ratio becomes particularly acute in regard to supercharged engines where there is an ever-increasing development of excessively high forces after the engine is started. The forces increase during warm-up and become maxiumum under high-load conditions. In regard to a diesel engine adapted for automotive use, there is a critically deficient power at low speeds while the maximum speed of the engine is usually around 4000 RPM's. In a diesel engine, the compression ratio must be at least 20:1 and even 25:1 to start an engine. However, a compression ratio of this magnitude becomes a detriment during supercharging and maximum load conditions. This is because the pressure in the cylinder does not remain constant. During start-up, there is polytropic compression leaning toward the isothermal-thermodynamic condition; while at full speed, there is polytropic compression leaning toward the adiabatic-thermodynamic condition. Moreover, supercharging increases the compression ratio.